Oliver Lehnert

Friedrich-Alexander-University of Erlangen-Nürnberg | FAU · Geo-Center of Northern Bavaria, Department of Lithosphere Dynamics

Understanding ancient climate changes is hampered by the inability to disentangle trends in continental ice volume from records of relative sea-level change. As a unique coastal deposit in tropical and subtropical regions, beachrock has been proved to be reliable for constraining the glacial meltwater signal and thus the total volume of land-based...

New conodont and stable isotope data are presented from the classical Baizitian section in the Yanbian County of the Sichuan Province, South China. The Telychian to Sheinwoodian strata were sampled and studied for carbon isotope stratigraphy and conodont biostratigraphy. The paired δ13Ccarb and δ13Corg data reveal a pronounced positive excursion, t...

We provide a stratigraphic assessment of the Upper Ordovician through lowermost Silurian of the Stora Sutarve drillcore from southernmost Gotland. Based on the combined information from lithological characteristics and carbon isotope chemostratigraphy we document a sedimentary succession tentatively ranging from the Kinnekulle K-bentonite near the...

The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project aims to characterise the structure and orogenic processes involved in a major collisional mountain belt by multidisciplinary geoscientific research. Located in western central Sweden, the project has drilled two fully cored deep boreholes into the bedrock of...

We present a δ 13 C carb chemostratigraphy for the Late Ordovician Hirnantian Stage based on 208 whole-rock samples from six outcrops in the Oslo-Asker district, southern Norway. Our data include the Norwegian type section for the Hirnantian Stage and Ordovician-Silurian boundary at Hovedøya Island. The most complete record of the Hirnantian Isotop...

SUPPLEMENT S1.-Response of organophosphatic brachiopods to environmental changes during the Lau/Kozlowskii Bioevent and the Mid-Ludfordian glaciation Mergl et al. (2018) described the stratigraphical distribution of organophosphatic brachiopods from the uppermost part of the Neocucullograptus inexpectatus to the lower part of Monograptus parultimus...

The present study reviews the main geochemical, sedimentological, and paleontological events associated with one of the largest perturbations in the Phanerozoic carbon cycle, the Mid-Ludfordian Carbon Isotope Excursion (MLCIE), which is globally documented in Late Silurian marine successions. Climate changes associated with the MLCIE are not yet we...

Results of conodont-based δ¹⁸Ophos studies from two core sections in Estonia (Mehikoorma-421 and Valga-10) indicate that the pre-Hirnantian Late Ordovician was characterized by a general cooling trend: a rapid climate cooling in the early Sandbian and a less intense cooling in the late Sandbian through Katian. During this time interval, sea-surface...

The Cambrian succession of the Tingskullen drill core from northern Öland comprises Cambrian Series 2 and Miaolingian (Wuliuan Stage) siliciclastic strata. The major portion of the succession is represented by the Miaolingian Borgholm Formation, which, in ascending order, is subdivided into the Mossberga, Bårstad and Äleklinta members. The Äleklint...

The Ludfordian (late Silurian) records one of the largest perturbations in the Phanerozoic marine carbon cycling, the mid-Ludfordian positive δ¹³Ccarb excursion (MLCIEcarb), which occurred in the aftermath of the Lau/Kozlowskii Bioevent (LKB). There are still controversies regarding origin of the MLCIE and its possible causal link(s) with respect t...

Variation in the relative abundance of the stable carbon isotopes has been widely used to correlate Ordovician marine successions over the past two decades. To date, only a few of studies of Ordovician carbon chemostratigraphy have been conducted in South China. Most of the previous studies in this field have focused on specific time intervals and/...

The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions with tropical water surface temperature estimates, interpolated from oxygen isotopes, approaching 40 °C. In the mid-latitude Baltoscandian Basin, conodonts displaying low δ18O values, which suggest high temperatures (>40 °C) in the water column, are in c...

Introduction: Early Ordovician (Floian) lithistid sponge-Calathium-microbial reefs were discovered in the lower part of the Lower Setul Limestone in Perlis, northwestern Malaysia Peninsula. Results: With a thickness of more than 30 m, massive microbial boundstone is surrounded by thick-bedded oncoid-intraclast rudstone/grainstone. The reefs were co...

The Swedish island of Gotland is located within the Baltic Basin. During the Late Ordovician the region around Gotland was part of a shallow epicratonic basin in the southern subtropics. In these warm-water environments algae flourished, diverse reefs developed close to the coastline and further outboard carbonate mounds developed. These mounds for...

In Scandinavia, the boundary between provisional Cambrian Stage 4 and the Wuliuan Stage is marked by a prominent unconformity ascribed to non-deposition and erosion during a eustatic sea-level fall that may partially correlate with the regressive ’Hawke Bay Event’. Wuliuan strata are widely distributed in Scandinavia, but exposures are relatively f...

The Fezouata Lagerstätte, discovered in the Lower Ordovician rocks of Morocco, is a Konservat-Lagerstätte of prime scientific importance. It provides access not only to the ‘shelly’ (skeletonized) part of its fossil assemblages, but also to non-biomineralized to lightly sclerotized organisms and to exceptionally preserved soft tissues of a complex...

The Komstad Limestone forms a distal part of the widespread ‘orthoceratite limestone’ of the Baltoscandian continent. In this paper, we present an integrated conodont biostratigraphy and carbon isotope stratigraphy for a major part of this formation and address its significance for evaluating Middle Ordovician correlation and overall stratigraphy....

The Late Devonian Siljan Ring structure in Sweden is the largest known impact structure in Europe. The present-day structure comprises a central dome that is about 20–30 km in diameter, which is surrounded by a ring-shaped depression. In this study, we focus on the southwestern part of the Siljan Ring with the aim to map the structure of the Paleoz...

After shifting into Icehouse conditions in Middle Ordovician times, the Late Ordovician is characterized by intensive glaciations of south-polar Gondwana accompanied by major regressions subaerally exposing wide areas of low-latitude palaeocontinents covered by epicontinental seas. The exposure of carbonate platforms led to their widespread karstif...

The positive δ¹³C excursion associated with the Late Silurian Lau Event is recognized globally and is the most prominent carbon isotope excursion of the Phanerozoic. We present new δ¹³C data (195 samples) and the first continuous carbon isotope stratigraphy across the stratigraphic range of this bioevent based on two drill cores from Gotland, the i...

The widespread growth of reefs formed by a framework of biogenic constructors and frame-lacking carbonate mounds began on Baltica during Ordovician time. Previously, Ordovician reef and mound development on Baltica was considered to be sporadic and local. A review of all known bioherm localities across the Baltic Basin reveals a more consistent pat...

The first Ordovician micromorphic linguliform brachiopods are described from the Province of Mendoza of west-central Argentina. The focus of the study is on carbonate successions exposed in the San Rafael Block, south of the famous Precordillera of San Juan, La Rioja and Mendoza representing the largest area of the so-called Cuyania Terrane. In the...

Late Ordovician mud-mounds in the Boda Limestone, Siljan area, central Sweden, consist mainly of massive spiculitic stromatactis limestone similar to other well-known Paleozoic mud-mounds. The mound cores are predominantly formed by spiculite and ostracod-rich mudstone and/or wackestone, and networks of spar-filled syndepositional cavities. The mou...

This study documents conodont faunas of the Fezouata Formation, recovered from the AZ-1 borehole at Adrar Zouggar Mountain and from outcrops near Zagora in south-eastern Morocco. The Fezouata Formation was deposited on the peri-Gondwanan shelf near the South Pole during Early Ordovician times. It is composed of mostly fine-grained siliciclastics an...

One of the few and most complete records of the MDICE (Middle Darriwilian Isotope Carbon Excursion) is herein documented from Baltoscandia. Based on a core section penetrating the condensed Lower–Middle Ordovician succession (~46 m) on the island of Öland, southeastern Sweden, we provide an integrated scheme for carbon isotope chemostratigraphy (31...

The limestones of the upper Katian Boda mud mounds (Ordovician) of the Siljan district in central Sweden are deeply fractured. The fissures were partly synsedimentary and are often lined with stromatolite-like crusts. These crusts thus far are the only known subaerial Ordovician speleothems. They reach depths of up to 30 m below the former mound to...

The δ13C record from an early Sheinwoodian limestone unit in the Prague Basin suggests its deposition during the time of the early Sheinwoodian carbon isotope excursion (ESCIE). The geochemical data set represents the first evidence for the ESCIE in the Prague Basin which was located in high latitudes on the northwestern peri-Gondwana shelf during...

The province of Jämtland, central Sweden, records a well-preserved but very thin suite of the Lower–Middle Ordovician cool-water carbonates. In this study we present the first carbon isotope profile for these strata on the basis of whole-rock samples from the Brunflo 2 core. The studied succession is 41.55 m thick and includes, in ascending order,...

The limestones of the upper Katian Boda mud mounds (Ordovician) of the Siljan district in central Sweden are deeply fractured. The fissures were partly synsedimentary and are often lined with stromatolite-like crusts. These crusts thus far are the only known subaerial Ordovician speleothems. They reach depths of up to 30 m below the former mound to...

Based on δ 13 C data from two drillcores recovered from the Siljan district, we present a first continuous carbon isotope record of the upper Tremadocian–lower Katian limestone succession of central Sweden. New names for some isotopic carbon excursions from the Cambrian–Ordovician boundary through the basal Darriwilian are introduced. The Mora 001...

Reefs developed simultaneously during the latest Sandbian/earliest Katian global Guttenberg Isotopic Carbon Excursion (GICE) in several places across Baltoscandia. Latest Sandbian/earliest Katian patch reefs are also described from the Vasalemma Formation of northern Estonia. The Saku Member of the Vasalemma Formation was previously considered as a...

The Vasalemma Formation (early Katian, Late Ordovician) of northern Estonia consists of a succession of biodetrital grainstones up to 15 m thick with numerous intercalated reef bodies, which reach diameters of more than 50 m. Four dominant facies types are distinguished within the reef core limestones: (1) a bryozoan framestone—bindstone, (2) an ec...

Based on the Tingskullen drillcore, we present the first continuous carbon isotope stratigraphy from the Lower–Middle Ordovician “orthoceratite limestone” of O¨ land, Sweden. The extremely condensed Tremadocian and Floian stages include large gaps as well as the Ceratopyge Regressive Event and the widespread Evae transgression accompanied by promin...

In western Laurentia a thick Paleozoic succession is exposed that shows repeated paleokarst development. Karst events culminate within the Ordovician towards the top of the Sauk megasequence. Concomitantly, there is a systematic increase in depth of erosion and intensity of weathering from the base of the System towards the Mohawkian. After deposit...

A more than 2000-m-thick Cambrian^Ordovician carbonate platform succession developed on the exotic Argentine Precordillera terrane during rifting from Laurentia and drifting towards Gondwana. On base of these carbonates, a carbon isotope curve could be developed for the Cambrian^Ordovician. We measured Delta13Ccarb and Delta13Corg values on bulk ro...

Exposures are very limited in the Siljan impact structure and contact relations of most units are not visible. Drill cores are the only useful tool to discover the complex geological history of this area where the sedimentation on the Proterozoic basement started during the late Tremadocian and lasted at least until the Late Silurian with the depos...

The Concentric Impact Structure Project (CISP) focuses on the two best-known craters on the Scandinavian Peninsula - Siljan and Lockne. They are primary models for concentric impact structures, i.e. craters with a shallow, outer crater developed in a weaker/less dense upper layer surrounding a deeper crater in the crystalline basement. The effects...

The Stumsnäs 1 core, drilled in 2011 in the southern part of the Siljan Ring, represents a structurally complex section and provides new insights into the impact-induced local structure in central Sweden. The Siljan Ring was formed around the central uplift of a Late Devonian meteorite crater, the largest known impact structure in Europe. The Stums...

The facies development through the stratigraphical interval of the Silurian (late Ludlow) Lau Event and the associated major δ13C record excursion have been studied in the Prague Basin. The investigated sections consist of temperate-water carbonates (Kopanina Formation) that were deposited in shallow as well as deeper parts of the basin. In both ar...

Several prominent palaeokarst surfaces have recently been detected in the Cambro-Ordovician sedimentary succession of Sweden. The oldest palaeokarst was found in autumn 2011 in Västergötland. An irregular palaeokarst cave with a breccia fill yielding large, angular Orsten clasts in a dark mud- to wackestone matrix is exposed beneath a karstic surfa...

The Stumsnäs 1 core, drilled in 2011 in the southern part of the Siljan Ring, provides new insights into the stratigraphy of the Ordovician succession in central Sweden. The core section shows evidence of the structural complications caused by the late Devonian meteorite impact in the area. In the core, about 90 m of Tremadocian to Darriwilian stra...

New oxygen isotope data from the Prague Basin document drastic climate changes from a cold interval during the early Přídolí followed by moderate to rapid warming and development of supergreenhouse conditions during the late Přídolí transgrediens graptolite Zone. This extremely warm climate presumably triggered the flooding of northern Gondwana she...

2013): Conodont biostratigraphy in the Early to Middle Ordovician strata of the Oslobreen Group in Ny Friesland, Svalbard. [Conodontenstratigrafi e im Unter-und Mittelordovizium der Oslobreen-Grup-pe in Ny Friesland, Spitzbergen. Abstract: The remotely located Cambro–Ordovician strata in Ny Friesland, NE Spitsbergen, Svalbard, are referred to the O...

Cruziana ichnospecies have been repeatedly reported to have biostratigraphic significance. This study presents a re-evaluation of the arthropod ichnotaxa of the Cruziana rugosa Group from bio- and/or lithostratigraphically well-defined Lower to Upper Ordovician siliciclastic sections of southern and central Bolivia. With the exception of Cruziana r...

Siljan is Europe’s largest impact structure and preserves unique Lower Palaeozoic sedimentary successions in its ring-like depression around the central uplift. Outcrops are limited, but the Lower Palaeozoic stratigraphy investigated in three core sections provides new information revolutionizing the knowledge of the development of this area locate...

The facies development through the strati-graphical interval of the Silurian (late Ludlow) Lau Event and the associated major d 13 C record excursion have been studied in the Prague Basin. The investigated sections consist of temperate-water carbonates (Kopanina Formation) that were deposited in shallow as well as deeper parts of the basin. In both...

Organic geochemical assessment of seep oil from the Upper Ordovician (Hirnantian) Boda Limestone and solid bitumens from the Middle Ordovician (Darriwilian) limestone formations in the Siljan Crater, Sweden indicates their generation primarily from peak oil window maturity, clay-rich marine source rocks that contained aquatic algal organic matter a...

Two new reflection seismic profiles over the Paleozoic successions of the western part of the Siljan Ring impact structure show a contrasting seismic signature. The more southerly c. 10 km long Mora profile reveals a highly disturbed structure, with only a few kilometers of relatively horizontally layered structures observed. However, interpretatio...

During the last two decades it became evident that the Silurian was a period of major climatic changes. There are classic studies on the Gotland carbonate successions where Llandovery through Ludlow faunal extinctions, sedimentological changes and isotopic events have been intensively studied and there are many reports from coeval events in other p...

The Silurian was a period of major climatic changes, faunal overturns, drastic sea-level fluctuations and platetectonic reorganisations. Llandovery through Ludlow faunal extinctions, sedimentological changes and isotopic events have been intensively studied on Gotland and in other parts of the world. For Pridoli strata limited information is availa...

New drill cores from the largest known impact structure in Europe, the relict of the Siljan meteorite crater, provide new possibilities to reconstruct Early Palaeozoic marine environments and ecosystems, and to document changes in sedimentary facies, sea level and palaeoclimate in Baltoscandia. The impact crater is an important target of the projec...